text:
How many 747-200 are still in service?
I'm wondering how many 747-200's are still in service?
I know for sure Rolls Royce is using one for testing purposes.
And the one from the US Forces.

Are there any civilian operated ones left?
Does somebody have photos?

Running the numbers from RedGrittyBrick's answer, there appear to be 36 active 747-200s out of 393 built (according to Wikipedia). Of the 36, 9 are passenger planes, 22 freight (including 6 converted from passenger planes, marked *), 3 combi (passenger and freight), and the two VC-25As ("Air Force One").
The active aircraft are as follows, with tail numbers included so you can look for photos.

Aerospace One: 1 freight (SX-ASO), 1 combi (SX-ASC)
AHS Air International: 1 freight (AP-BIO)
Cargo Air Lines: 1 combi (4X-ICM)
Caspian Airlines: 1 freight (EP-CQA)
Iran Air: 3 passenger (EP-IAG, EP-IAH, EP-IAI), 1 combi (EP-ICD)
Jet Star: 1 freight (ER-BBS)
Kabo Air: 3 passenger (5N-DKB, 5N-JRM, 5N-MAD)
Kalitta Air: 2 passenger (N715CK, N793CK), 4 freight (N704CK, N746CK, N794CK,* N795CK*)
Kam Air: 1 freight (4L-TZS)
Midex Airlines: 3 freight (A6-MDG, A6-MDH, A6-MDI)
Orient Thai Airlines: 1 passenger (HS-UTC)
Rayyan Air**: 2 freight (AP-BKI, AP-BKS*)
Saha Airlines: 2 freight (EP-SHB, EP-SHH)
Saudi Arabian Airlines: 1 freight (HZ-AIU)
United States Air Force: 2 VC-25A (82-8000, 92-9000)
Uni-Top Airlines: 3 freight (B-2448,* B-2450,* B-2462)
Veteran Avia: 1 freight (EK74799*)
Vision Air International: 1 freight (AP-BIV)

* Built as passenger and converted to freight.
** Not to be confused with Ryanair! :-)
There are also several stored aircraft, including the Rolls-Royce test plane you mention in the question.

Thanks to fooot for explaining that BSF denotes "Boeing Special Freighter", a passenger plane converted to freight use.

What did they do to the other ones?

@Firee Scrapped or in storage.

How many 747-200 are still in Service?

If you search Airfleets.net and, for all pages, add up the aircraft marked as active, you will get an answer.

Are there any Civilian Operated ones left?

If you mean non-military, the above method should tell you.
If you mean non-airline, I don't know how to find out easily. RR's N-787RR was hard to find at Airfleets.net.

Does somebody have Photos?

Almost certainly yes, I'd just Google the registration number. e.g. EP-SHB. They'll mostly be copyright protected of course.

As of 2022 (And what I'm aware):
Fly Pro: 1 freight (ER-BAR)
Fars Air Qeshm: (EP-FAA & EP-FAB)
Iran Air: (EP-ICD)
Kam Air: 1 freight (4L-TZS)
Fly Pro Cargo: 1 freight (ER-BAT)
Iran Air Force: 1+ Military (5-8106)
United States Air Force: 2 VC-25A (82-8000, 92-9000)
E4B: 4 Military
GeoSky: 2 freight (4L-GEN, 4L-GEO)
Aerostan: 2 Freight (EX-47001, EX-47002)
Sources:
planespotters.net/operators/Boeing/747/747-200
I did remove some that were on the list as they are stored IRL but stated as active on Planespotters.net.

Source, please?

https://www.planespotters.net/operators/Boeing/747/747-200
Here!
Edit: I did remove some that were on the list as they are stored IRL but stated as active on Planespotters.net.

For those who suggest edits to this post: without something authoritative (i.e. a source -- in other words a link to something stating that "this" 747-200 is no longer operating, for instance), suggested edits will probably be rejected, because without a source to check, such an edit is indistinguishable from vandalism.  If you have a document that demonstrates the truth of your edit, then please incorporate within your edit the link to that source, and it will probably be approved.


text:
What is the maximum range of a BAe 146-300? Can auxiliary fuel tanks be added?
What is the maximum range of a BAe 146-300? I saw one on Flightradar24.com which started in western France and is still flying non-stop to Greece (flight in progress at the time of posting).
I was really surprised, I guess they probably have an additional fuel tank? I know that some airlines do add extra tanks  to their planes (e.g. on a B737) to increase the maximum range; but is it possible on on a BAe 146-300?

these planes are colloquially known as "smurf jets"

According to wikipedia it has a range of 2909 km and the distance is around 2500 km

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sort: votes


text:
Where can I download the flight plan data around the world?
Where can I download the flight plan data around the world, so that I have analyze their route?
Are they provided freely?

Related: Is there a Flights API to get flight information months in advance? and How can I get flight destination from ADS-B?

Thanks. For flight plan data (not ADS-B data), is it monopolized by some companies but not publicly available?

The flight plan, as a list of waypoints etc, is proprietary information of the airlines or private pilots producing those plans. It is provided to the national and international authorities / flight services but I don't know if any of these organisations have any need to share them with the public. Obviously, in normal circumstances, travel agents and passengers only want to know the departure and arrival times and locations. Flight plans are also subject to change, for example to avoid weather.

For historical FAA IFR flight plan data, you can get it from www.flightaware.com.  They show five minute delayed, and with a free registered account you can get access to the last 90 days worth of data.  You can pay for data older than that and I believe in different data formats.
I'm not aware of a similar source for other parts of the world.

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Is it possible to calculating sea-level pressure with an unknown base station altitude?
I'm trying to program a BMP180 pressure/temperature sensor to calculate altitude.  The method I've seen used is to input your current base station altitude to calculate the sea-level pressure.  It seems a little tedious to input the base station altitude everytime, so I was wondering if it is possible to calculate sea-level pressure without a known base station pressure.
I've been trying to calculate sea-level pressure through iteration.  I would set the default sea-level pressure at 1013.25 mb, use this number to calculate an estimated altitude, use the estimated altitude as my current base-station altitude to calculate a new sea-level pressure, use this new number to calculate an estimated altitude, etc...  However, I noticed that my results are diverging.  Is there a better way to calculate the sea-level pressure?

Which information is available to you in this calculation?

I can measure temperature and pressure directly, those are the only two pieces of information available

Then you have no way of distinguishing between being at sea level in a low-pressure area, or up in the hills in a high-pressure area.

Yes, that was why I was trying to calculate sea-level pressure through iteration, hoping that it will converge to a number.  I guess I will either have to stick with relative altitude or input a known base-station pressure

Since your measured inputs in the two cases would be exactly the same, you have no hope of distinguishing them through calculation, iterated or otherwise.

oh! good point, I just blindly applied "iteration".  I will have to rethink this.

However you can get the sea level pressure for nearest airport (from http://weather.noaa.gov/pub/data/observations/metar/stations/ or many other places on the net). Except in storm or worse weather the gradients are not large, so using your nearest airport pressure should yield a reasonably precise altitude. Or switch to GPS, which gives you true altitude to several metres (depends on receiver quality) without any configuration (and then you can calculate sea level pressure e.g. for weather forecasting).

@JanHudec I think that might be the way to go.  My device isn't connected to the internet, so I will have to input it manually on every startup.  I might look into getting a GPS module.

Calculating sea level pressure depends on knowing your altitude.  A function that does this is the hypsometric equation $$\Delta z = \dfrac{R \overline{T}}{g}\ln\dfrac{p_1}{p_2}.$$  This function gives the depth ($\Delta z$) of an atomspheric layer with average temperature $\overline{T}$ between pressure levels $p_1$ and $p_2$.  In your case, the station pressure is known and the height of mean sea level is known; in order to calculate your height or to calculate sea level pressure, you must know the other quantity.  The average temperature is also an unknown, but you can approximate this or use a value based on the lapse rate of the standard atmosphere.

Since answers aren't really supposed to go in the comment area:
If all you have is ambient temperature and ambient pressure, and no elevation information, there is no way you can calculate sea-level pressure.
Credit for the content of this answer goes to Henning Makholm.


text:
What do these weather depiction chart symbols mean?
I have several present weather symbols from the weather depiction chart that I'm not clear on and AC-0045 doesn't have in it's legend.
I know the mist and fog symbols, and these look very similar, but I'm not sure what the broken lines imply.  I've added three variations on the symbol below.

Since the other user posted a link that contained the answer that could in the future go 404, I'll provide the answer I found there.
The first symbol means "Fog in patches"
The second symbol is not present but by extrapolations likely means either "Mist in patches" or "Mist with sky visible".  The former seems more likely to me.
The third symbol means "Fog, sky visible."


text:
Did Flight Engineers progress to be pilots?
When 3 man cockpits were common place on commercial aircraft what was the career progression of a Flight Engineer like?
Did FE's normally transition to be pilots? I'm not trying to insinuate here that FE's were in anyway inferior to the pilots and of course some FE's would of had no desire to transition to a pilot capacity at all.
Were there any airlines who operated a policy of starting flight crew out as a FE then training them as pilots?
N.B - Some background information that I'm basing this question on is I've read a number of reports regarding young (early 20 y/o FE's becoming pilots) and in maybe a more extreme case the hijacking of FedEx Flight 705 when the FE who hijacked the aircraft (an ex-Naxy pilot) had been made a FE (this could be part due to the fact he apparently falsified his Navy flying hours).

"Did" should maybe be "do" -- flight engineers are still found in commercial service, especially on cargo airlines.

I know a FE who went on to become a mechanic. I think this may be because he started a mechanic apprenticeship before becoming a FE

Before the turn of the century (I can't believe I'm using that phrase, as I retired in 1999) and especially back when all 3 engine and 4 engine airliners had a flight engineer, the usual career path at many airlines was to hire in as an Flight Engineer, or FE (two stripes), progress to an First Officer, or FO (three stripes), and then become a captain (four stripes).
This all began to change, of course, with the advent of large 2-man cockpit aircraft. The change was not without controversy and some pain. For example, at least one initial operator of the 737 ran a 3-man cockpit for a time. The 3rd guy was, as I remember, referred to as the GIB (guy in back). He sat in the jumpseat and read the checklists, which was one of the tasks an FE typically had in 3-man cockpits.
As it happened, the two jet carriers I worked for hired pilots into the FO seat and used professional FEs. I spent a couple of years on the 727 and then 10 years on the 747.  During that time, every FE save one that I flew with was ex-military, and with few exceptions all were A&Ps. That was desirable in case a maintenance sign off was needed when you were someplace where maintenance was not otherwise available.
Occasionally you would encounter an FE who had been a captain.  The pilots were required to retire at 60 back then, but FEs weren't.  I only knew one such individual, and I always liked flying with him.  The more expertise you have in the cockpit, the better.
In the two 747 carriers I worked for, an FE would sometimes transition to the FO seat, but that was relatively rare, and the costs were typically the individual's to bear.  Interestingly, when I retired in 1999, I had flown with an ex-military FE who years later became the chief pilot of the airline involved.

Many thanks Terry - I was hoping I would get an answer from you on this. Thats pretty much covers everything I wanted to know.

One additional point to a great answer; traditionally, flight crews were kept together with a relatively static senior "captain" and junior "first officer", but modern logistics, especially for domestic hops, often involve "mixed" flight crews. There are several reasons it's done, the primary one being reduced headcount, but the result is often that the pilot and copilot are of the same rank, and are referred to as "captain" and "co-captain". Both will have triple stripes and are fully qualified to lead any flight crew, but there has to be one guy in charge on the flight.

What is an "A&P"?

@davidbak Aicraft and Powerplant license. In other words a certified mechanic that can work on the airframe and the engine. Sometimes you'll still see A&E, Aircraft and Engine, which was the old way of referring to it. The FAA changed the wording, Engine to Powerplant, some years ago.

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text:
Is there any U.S. / FAA regulation that could apply for aviation software?
I want to build some software applications applied to the aviation industry and would want to know if any U.S. / FAA regulation could apply in the design of them.
I know there are some regulations when a software holds information related with finance, health or kids.

Great question, I'm also interested to know this.

Could you clarify what type of software are you referring to: software containing information about aircraft, or actual avionics software in aircraft?

@Quantas You are right. I was meaning to software containing info on databases like a pilot logbook website.

@LuisArriojas You might want to edit this question into dealing with aircraft systems software (which is the direction the answers took) and ask about flight-planning and E-Logbook software in two separate questions where we can go in-depth on them. There's some interesting regulatory "fuzz" surrounding logbooks already (in the US you don't need to keep a pilot logbook except to show currency) and easily a few hundred sources on "EFB"/flight-planning software we could really dig into :)

For simulators you have Part 60 of CFR 14
For airborne software the FAA has published AC 20-115, but the main document that refers to is the FAA/EASA RTCA DO-178/ED-12 currently at the "C" version: Software Considerations in Airborne Systems and Equipment Certification.
If you want to certify (and thus commercialize) your software for flight, this is the main document to read.
Depending on the scope of the software and the design/development process there might be different supplements (see here):

DO-330 Software Tool Qualification Considerations
DO-331 Model-Based Development and Verification Supplement to DO-178C and DO-278
DO-332 Object-Oriented Technology and Related Techniques Supplement to DO-178C and DO-278A
DO-333 Formal Methods Supplement to DO-178C and DO-278A

It has been prepared by the RTCA/EUROCAE joint committee and approved by both FAA and EASA under different names, but the content is the same.
Note that these documents are not freely available.

As an aside, the European versions are available from EUROCAE for a price.

@RedGrittyBrick you can post it in the relevant question

As a general statement, a number of software vendors making non-certified applications are sure to include big bold warnings that the software is only used to increase situational awareness and should not be relied upon for instrument conditions.
For example, the Garmin Pilot Manual has a number of disclaimers (most common sense) to remind you that it is not a substitute for other systems.
That said, as Qantas 94 Heavy pointed out, the answer is quite different for certified avionics, and that depends on which part of the FAR the aircraft is being certified under.
If you make something like an E6B app, you're probably in the clear.  After all, you would have just made some calculator with preprogrammed functions.


text:
Is aviation software translated into the users' native language desirable over English?
I want to build some software containing information about aircraft, like a logbook. Nothing related with avionics.
I know that default language in the aviation industry is English, but in the case of online software, could professionals be interested in using an online logbook or MRO software showing in another language besides English?

A native language version is very helpful for training. If people are confronted with new concepts AND new vocabulary to convey those concepts, their learning load is doubled. A native version of educational software would reduce the load and help the trainee to progress. The benefit of a native version for experienced pilots would be small, however.

English is the native language of aviation...
I myself always get mightily annoyed at poorly translated software, which is 90% of all software provided in multiple languages. IF you provide multiple languages, allow the user to switch between them AND get professional translators to do the work.

Would it sell? Probably, if it's good enough. But I don't see the language options as being a major selling point. Certainly not so big that having them will make a large number of potential customers choose it over another product that has more options elsewhere but lacks language selection.
In some places maybe, where English is less than common and not generally used by ATC.
Whether that's where your intended market is I don't know.


text:
Is "right-of-way" based on aircraft size?
I was speaking with an ATP-rated pilot the other day, and he said something that sounded odd: basically the bigger aircraft has right of way once airborne.
Can anyone shed some light on this? As far as I understand, ATC coordinates the landing/departing aircraft; at least at my airfield where there was MD80's, B738 and G/A.

possible duplicate of Which way should you turn to avoid another aircraft?

The rules for right of way are rather clearly defined. Basically, you give way to the aircraft on the right; and powered aircraft always give way to unpowered aircraft (i.e. gliders), and all give way to uncontrollable aircraft (like hot air balloons). I've never heard that size of the aircraft matters.

@ratchetfreak the answer is available in the other question, the question itself isn't a duplicate though.

I guess as a rule of thumb you could say the less maneuverable an aircraft is, the more aircraft have to give way to it.

@Maverick283 That is correct.

If you want to take up a Cessna and pick a fight with a 747, be my guest.

The size of an aircraft plays no role in identifying who has right of way.
The general rule is that for same-class/type (powered or non-powered) aircraft, the aircraft coming from the right has right-of-way and should be yielded to. This is irrespective of the size within the same type, but a question of manoeuvrability. For different types of aircraft, a powered aircraft will have to yield to non-powered aircraft. For more details see the related question below, ICAO Annex II, FAR 91.113 or another explanation in the Skybrary.
Technically, this means that where separation between IFR and VFR traffic is not provided and aircraft on both flight rules can operate, a Boeing 737 would have to yield to any powered or non-powered aircraft coming from the right.
In most jurisdictions you will find a passage that also details that aircraft should give way to other aircraft that are established on final approach, so a strong situational awareness in the vicinity of airports and airfields is required. Whether separation is provided between IFR and VFR within a traffic pattern, is based on the jurisdiction and the airspace class. In most cases of smaller general aviation aircraft and larger/faster general aviation or commercial aircraft operating at uncontrolled airfields, the smaller aircraft will yield to the faster traffic already on the final approach path out of courtesy or due to good airmanship. It is easier and also cheaper for a smaller general aviation aircraft to perform a 360° turn than for e.g. a Learjet on final approach.
See related question: Which way should you turn to avoid another aircraft?.
See also this YouTube video: Airplane Right-of-Way Rules - Author: Humble Aviation

+1 From a legal standpoint, this answer is correct. I would note that in uncontrolled areas, though, it seems relatively common (at least here in the U.S.) for smaller/slower GA aircraft to offer to allow larger/faster aircraft ahead of them, even if the smaller aircraft would normally have had the right-of-way. E.g. A Cessna or Cherokee pilot will often offer to let a Lear land ahead of them if normal sequencing would have otherwise forced the Lear to do a 360 or some such thing to maintain separation. It's a lot cheaper for a Cherokee to fly in a circle than for a Learjet to do so.

@reirab I will edit my answer to include "Good Airmanship" tomorrow morning.

That's not airmanship, its courtesy

@rbp I have worded my answer as such. This will be subjective, but "good airmanship" to me includes a good dose of courtesy.

"Airmanship can be defined as:[2]
A sound acquaintance with the principles of flight,
The ability to operate an airplane with competence and precision both on the ground and in the air, and
The exercise of sound judgment that results in optimal operational safety and efficiency."

@rbp That is a purely academic definition of it, it varies from my own definition.

Courtesy: ": polite behavior that shows respect for other people"

The airborne aircraft right-of-way rules are based on maneuverability, not size. Balloons get first pass, then gliders, airships, powered parachutes & hang gliders, then powered aircraft.
Exceptions include towing or refueling aircraft have right of way over the above, and anyone who declared an emergency has nominal right-of-way over them. Although I don't see the balloon rapidly departing the area just because someone said Mayday.
In practice the bigger aircraft will have right of way. A 747 just doesn't change course all that quickly but a Gulfstream will.
ATC sequences arrivals and departures on a first-come, first serve basis with allowances for wake turbulence - they won't have a Cessna land immediately after a widebody.


text:
How to hold the heading on the Boeing 777 autopilot?
I have X-Plane 10 with Boeing 777 Worldliner Pro- Extended Pack, which is designed to model the real-world operation of the 777.
Why does the AP never go to the heading hold direction even if I press the hold button?

Pressing the heading hold button will assume the current heading.
Pressing heading select will follow the course as selected in the display; this can be set by pressing the rotary encoder. It is also visible on the heading bug.

The Boeing 777 primary flight display will display HDG SEL and HDG HLD for each selection respectively.

"Heading Hold" is installed mostly for ATC purposes. Generally to insure horizontal separation between two aircraft.
The pilot will receive that kind of message : "XXXXX...maintain present heading".
It has not been designed to intercept the displayed heading.


text:
Why shouldn't you use HF radio while refueling?
FCOM limitations for many aircraft state:

DO NOT USE HF RADIO WHILE REFUELING

Why is this? I have heard from people that it's because most of the big airliners have a 'notch' antenna for HF; it's a small notch cut at the base of the vertical stabiliser. HF transmission power is fed to this notch and the whole fuselage acts as an antenna,
radiating the power.
Can someone explain in detail and in simple terms?

The safest way to refuel an aircraft is with everything turned off and the airframe grounded (or bonded) to the fueling system.  This is often not practical (particularly for airliners), so a number of other rules exist to make refueling as safe as possible -- not using HF radio while refueling is one of them.

So why is the HF radio singled out? Power, combined with the antenna design factors you mentioned.
With small radios you can easily light a fluorescent lightbulb (incidentally this is why radio geeks are such great fun at parties). HF radios can put out several hundred watts of power - this makes them more likely to generate a spark that can jump the gap between say a refueling nozzle and the refueling port/tank, igniting fuel vapors and ruining everyone's day.
HF antenna designs which use the aircraft itself to radiate part of the energy can further increase the chance of a spark.

Yes, at the free end of the HF antenna are voltages of several hundred to some kilovolts. With hundred watts the HV can reach levels to start fluorescent lamps and that is also enough to spark into free air. With some fuel dust it is like an electric detonator and TNT...


text:
What is the wing angle of attack of a Boeing 737 in cruise?
I would like to know the angle of attack that a 737 flies at during cruise. I am specifically interested in the wing angle of attack (if you know the cruise nose-up attitude and the wing incidence angle, that would be good too).

This Boeing Aero article about angle of attack might be of interest to you.

Won't the AOA in cruise vary according to factors including weight, position of CG, and air density (that would need to be specified)?

@mins I know what it depends on. I need a definite answer from someone who knows for sure, either by having piloted these, by having spoken to someone who has piloted these, or by being someone who has worked on these or has talked to someone who has worked on these. Derivations and conjecture formulation do not interest me.

My comment was to emphasize that you need to provide other elements that have an influence on the value, if you want someone to provide a value.

If I needed to provide other elements, I could obtain the answer myself, in theory. I think the main question of this thread is explicit, as the 737 has a specific cruise altitude and speed. An average value throughout the cruise segment would be sufficient. Ask a pilot: he will not ask you for the other elements, he will just tell you what AOA he adheres to as he flies from Hartsfield-Jackson to LaGuardia.

@Flanker Errr... no. They‘ll tell you an approximate range (which of course might be narrow enough for you to not care pragmatically).

By the way, if you happen to find a 737 QRH (quick reference handbook) somewhere, there should be some tables labelled Unreliable Airspeed. These contain pitch angles, speeds and power settings for various scenarios.

First, let's assume that all lift is created by the wing, and that the plane is flying in ideal conditions, where fuel flow per distance flown is minimal. This point is given by $$c_L = \sqrt{\frac{1-n_v}{3+n_v}\cdot c_{D0} \cdot \pi \cdot AR \cdot \epsilon}$$ Please see this post for more background on this formula.
Nomenclature:
    $c_L \:\:\:$ lift coefficient
    $n_v \:\:\:$  thrust exponent, as in $T \sim v^{n_v} $
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing
    $\epsilon \:\:\:\:\:$  the wing's Oswald factor
    $c_{D0} \:$  zero-lift drag coefficient
The $n_v$ I would estimate to be -0.4, the $c_{D0}$ is somewhere around 0.016, the aspect ratio can be taken from this source and the Oswald factor is 0.8. This gives you an optimum lift coefficient of 0.445. Now we need to know what angle of attack is needed for this lift coefficient. If we look at the midspan airfoil of the 737, this angle of attack is around 2.8 degree.

This source is for model airplanes, so their Mach and Reynolds numbers are much too low for the real thing, and we need corrections for both. Using the Prantdl-Glauert rule for Mach effects, we need to correct by dividing with $\sqrt{(1-Ma^2) \cdot (1 + tan\varphi)}$ = 0.693 at Mach 0.82. Please note that this increment must be applied to the zero-lift angle of attack, which is -1°. Now our angle of attack is only 1.63°. The flight Reynolds number of the 737's MAC is 22 million, so the angle of attack is even less, maybe 1.5°. Now we need a correction for the 737 wing sweep of 25 degree, which is computed by dividing the angle of attack by 0.9, the cosine of the quarter chord sweep angle. This gives about 1.8° as the corrected value.

So my quick-and-dirty answer is 1.8 degrees. Other sections of the wing have slightly different values, according to the wing's twist. Please note that the wing area of the 737 is roughly constant since the Sixties, while the mass has increased considerably. It is safe to assume that it is operating at higher angles of attack than the optimum for best range.

@ Peter Kampf
Thanks for the calculation, although I was looking more for an answer from the 'field', and not an estimate (I've got those already). Thanks anyway.

For that, assume that the fuselage incidence is exactly 0 at cruise, so that serving the meals is not inconvenienced. Now you need only to see which incidence the wing has, and you know your flight angle of attack. What is your result?

@PeterKämpf the fuselage incidence is usually designed to be > 0 in cruise. This is to prevent cruising at floor angles < 0 when the aircraft is very light and/or faster than the long range cruise speed. Fuselage angles less than 0 degree are uncomfortable.

If you are lighter, you should fly higher, and flying faster than optimum cruise quickly brings you to your Mach limit. I do not think that your design floor angle is much different from 0.

Aerodynamically speaking you are right, but aerodynamics are not the only factor that come into play when selecting cruise altitude. Sometimes you can't climb because of ATC restrictions. Sometimes you need to fly as fast as possible to ensure passengers will make their connections, basically putting you around FL260 - FL280 where you can make the best forward speed.

@DeltaLima: Yes, you may fly at a lower angle of attack, but the difference will be small, maybe 0.2 to 0.3 degree. Then, the reason you give is not the design case. And I would assume my error by using the optimum lift coefficient is bigger than that, given that the wing was designed in the Sixties for a much lighter aircraft with different engines, so all the parameters in my answer changed between then and now.

@Peter Kämpf, to clarify: I'm not looking for assumptions or calculations (I can do those myself). I am looking for a definite answer from someone, who is knowledgeable about the 737.

@Flanker The answer given by Peter will be in the ballpark. There are variations from flight to flight due to differences in payload, cruise speed and cruise altitude. The typical nose up attitude in cruise is between 2 and 4 degrees for the 737, so if you find the angle of incidence you can work it out.

@DeltaLima It is indeed. I just want a verification from someone who knows for sure. I'm running CFD tests, and I would rather have a more exact value than a ballpark value, since the CFD runs take quite a while, and I don't have too much time.

@Peter Kämpf The wing area was increasing with each generation of 737: Original - 102.0 m2, Classic - 105.4 m2, NG - 124.58 m2. I'm not sure about MAX. Sourse - b737.org.uk/techspecsdetailed.htm.

Late to the party, but I will add my comment from experience. The B737-800WL (winglets) has an optimum Cruise Body Angle of 2.46 degrees Nose Up where the non-winglet version has optimum at 2.53 degrees. This attitude in cruise is associated with Long Range Cruise (LRC) for any given weight. Constant Mach Cruise Nose Attitude will vary with aircraft weight, while if flown at airspeed/Mach consistant with LRC for weight the AoA remains constant.
The Minimum Maneuver Speed for any given weight is normally 5 degrees Nose Up in Level Flight. Any higher attitude (e.g. 8 degrees) would indicate flying at an unsafe angle of attack with reduced buffet margin.

Once you earn enough reputation you will be able to comment on a post.  This would be better as a comment.

@dalearn I think this is fine as an answer, and does not need to be a comment at all. By the way, user37299, answer here can be sorted in different ways (votes, oldest, latest edit), so "the answer above" does not work on this website. I will edit it out for your convenience. Welcome to Aviation.SE!

Do you have a source for this information?

The angle of attack on a 737 in cruise at 41000 is about 8 degrees on average.  A heavier plane will need a degree more.  A light one, about a degree less.  Keep in mind that airliners have a significant amount of wing twist, so I am only referring to the average angle of attack, not the AOA of the wing root or wing tip.

Welcome to SE Aviation. A reference for your statement would be welcome.

This answer is, from my experience flying the 737, wildly inaccurate. @Peter Kampf’s answer matches what I’ve observed.


text:
How to decode this Notam?
I've a difficulty to use the Notam decoder on this Notam.
V0018/24 NOTAMN
Q) OOMM/QPIAU/I/BO/A/000/999/2336N05816E005
A) OOMS
B) 2401250001
C) 2405160001
E) [US DOD PROCEDURAL NOTAM] INSTRUMENT APPROACH PROCEDURE NOT AUTHORIZED ILS RWY 08L.

Also what is US DOD in this context?

V0018/24 NOTAMN Q) OOMM/QPIAU/I/BO/A/000/999/2336N05816E005 A) OOMS B) 2401250001 C) 2405160001 E) [US DOD PROCEDURAL NOTAM] INSTRUMENT APPROACH PROCEDURE NOT AUTHORIZED ILS RWY 08L

In short

The Notam says the IFR approach for ILS RWY 08L at Muscat International Airport (Oman) is not allowed until 16/05/2024 00:01 UTC.

US DOD ➫ US Department of Defense. The DoD issues this Noram because there is an agreement allowing the United States, which have an important naval base in Oman, to use Oman's Muscat military airfields.

How to decode

V0018/2024 NOTAM ➫ Notam reference, N ➫ New Notam
Q ➫ Always Q

OOMM ➫ Related to Muscat control center (Oman)
QPIAU ➫ Instrument procedure is not available (Q ➫ QCode, PI ➫ Instrument approach procedure, AU ➫ Unavailable)
I ➫ IFR
BO ➫ Purpose: B ➫ Immediate attention, O ➫ flight operations
A ➫ Scope is the aerodrome
000/999 ➫ From sea level to unlimited
2336N05816E005 ➫ Center position is 23°36'N 058°16'E, radius 5NM (this is the reference point of the aerodrome)

A field ➫ Location, aerodrome or FIR, OOMS ➫ Muscat International Airport (Oman)
B field ➫ Beginning, 2401250001 ➫ Valid from 25/01/2024 00:01 UTC
C field ➫ End, 2405160001 ➫ Valid to 16/05/2024 00:01 UTC
E field ➫ Notam text, [US DOD PROCEDURAL NOTAM] INSTRUMENT APPROACH PROCEDURE NOT AUTHORIZED ILS RWY 08L

US DoD Notams are aimed to military and civil crews
It is a procedural Notam part of FLIP, issued by US DoD using DINS (which is interfaced with the AFTN). FLIP is a special information/documentation/mapping system provided by US agencies for foreign airfields. It is used by US military and also civil pilots via a subscription. This Notam is part of FLIP:

[...] Foreign civil/military flight crews who use US DoD FLIP should access DoD procedural NOTAM (V series) or DoD chart/FLIP/DAFIF NOTAM (W series). V/W series NOTAMs are available via:

Primary or secondary DINS Query websites.
Aeronautical Fixed Telecommunication
Network (AFTN),
[...]

(Source)

Most of this information can be decoded online.

US Department of Defense. This is alerting DoD aircrews that they may not fly this procedure.

It does make me wonder if Oman has put out a matching civil NOTAM for that ILS at Muscat...

A DoD procedure NOTAM does not have to be against a military procedure. Rather, it is issued when DoD aircrews may not use that procedure published in FLIP, as mins explained in his answer.

Yeah, I asked my question because I'm wondering if the issue is that the procedure somehow is nonconformant with US DoD standards in a way that renders it unflyable for DoD users but isn't an issue for civil air traffic, or if the procedure is NA because, say, the localizer transmitter is INOP, meaning that it's not usable for civil traffic either and Oman would have a civil NOTAM out saying that civil users can't fly the procedure either

DoD will not write a NOTAM against a procedure if the host nation has already written one.
While it is possible that a procedure does not conform to US standards, the likely result would be that it is not published in FLIP in the first place.

Let me also say that this should not be a DoD procedure NOTAM, since it is not a DoD procedure. Rather, the NOTAM should be a DoD FLIP and DAFIF one. It’s nuanced, but the DoD is not the procedure design authority.

Thanks -- that's the insight I was missing, that DoD won't NOTAM a procedure that the host nation's already NOTAMed.  It really does make me wonder what's wrong with the underlying procedure and its supporting NAVAIDs though...like, an ILS is an ILS is an ILS pretty much no matter where you go, no?

@UnrecognizedFallingObject, it’s possible that the procedure in DoD FLIP is out of date, so the office of primary responsibility writes a NOTAM until they can review & update the procedure in FLIP. That’s why I think this isn’t really a procedural NOTAM. That’s the speculation on my part.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Could Malaysia Airlines Flight 370 have sunk without leaving any floating wreckage?
With all the searching on the surface of the Indian Ocean for evidence of Flt. 370, I'm wondering if there's any conceivable scenario in which the Boeing 777 could have sunk without producing any floating wreckage.
Is it possible for a 777 or similar model to hit water without leaving a trace of remains on the surface?

possible duplicate of Can a commercial airliner sink to the bottom of the ocean?

@danny I disagree, that is about a intact water landing and sinking, this is about crashing in the water and not leaving any floating debris

Note that MH370 did leave floating wreckage.

Yes, but only under highly unlikely circumstances.  An airplane contains all sorts of materials that float, from fuel to seat cushions to the plastic cups in the galley.  In order to sink without leaving any floating wreckage, all of that material would need to be trapped within the airplane while it fills with water.
In order for this to happen, the airplane needs to land intact on the water.  As any number of ditchings indicate, this isn't going to happen -- even US Airways 1549 had the rear of the fuselage tear open on landing.  More often, the engines or wings will tear off, leaving oil and fuel slicks.

all of which debris will sooner or later (and most likely sooner) become waterlogged and sink. Depending on environmental conditions that may only take minutes. And that includes the oil slicks which, especially in warm water, can dissipate very rapidly.

@jwenting not all debris: for example a seat cushion / flotation device or an (even partially) inflated lifejacket will float for a long time.

@yankeekilo yes, for quite a while, but not indefinitely. And in rough seas not very long at all. They're also liable in rough seas or harsh sunlight to be damaged to where their floatation properties are compromised.

"In order for this to happen, the airplane needs to land intact on the water." Which would likely leave survivors able to use the slides as rafts, among other things.

US Airways 1549 landed on calm water. There is no way to land a large jet intact on any significant waves and there are always waves in the middle of an ocean.

@AdamDavis - assuming they're still alive and conscious. In the case of MH370 there's reason to believe they weren't.

@JanHudec there are always waves, but define "significant" - the sea can be very calm and in many areas has low, slow rolling waves which would not pose any intrinsic threat

@JonStory: Slow-rolling does not matter, only height between highest and lowest point does. I don't know at what height it they start to make a problem, but it won't be that much. Because if the plane bounces of the first wave, it will come down too hard and if it hits a wave at one side, it will start to turn and both are likely to break it apart. It will often be survivable, but it will make getting out seriously difficult for some.

Not slow-rolling, slow + rolling: as opposed to choppy, fast and high. I'm not saying a jet can or should land on waves, just that the sea can sometimes be very calm indeed. You said that a jet can't land on "significant" waves and that there are "always" waves in the ocean, but there are not always "significant" waves

Yes, it's certainly possible. But it all depends on a lot of factors.

Speed of impact. Obviously, the lower the speed of impact the fewer pieces will break away.
time. Even if things break away and float, after a while they'll sink as they become water logged. And that may only take minutes.
environmental conditions. Water temperature affects the speed at which chemical spills dissipate. So do wind and currents. Wind and currents, through wave action, can also break up into tiny fragments and cause to sink any floating debris.

So even if something were left on the surface after the impact, after a few hours most of it would be gone. After days, unless the aircraft crashed near a shore and pieces wash up, most likely there's nothing left to see unless very large pieces broke off and managed to stay afloat (which would require very calm surface conditions indeed).

Not everything that becomes waterlogged sinks. Consider something like a foam seat cushion: if the material the foam is made from is less dense than water, it will continue to float even if the air bubbles become full of water.

@DavidRicherby until its deteriorated by wave action, salt corrosion, and sunlight to the point where it breaks up.

Sure but that takes much more than a few hours. Many synthetic materials take years to biodegrade, even in relatively hostile environments. Plastics, for example, don't care if you cover them in salt. If the plane broke up when it hit the water, parts of it will remain afloat for a very long time; the problem is that the parts will disperse over a huge area.

It may possible like the US Airways Flight 1549 ditched in the Hudson River

This was in a river with smooth water. I'm not sure if there's ever been a passenger jet successfully land intact on the sea.
If the Malaysian flight successfully ditched like Flight 1549, then I'm not sure if the plane could float for hours. It would sink for sure if the doors were opened.

I'm no expert but Airbus and Boeing have fairly different philosophies when it comes to automation. The Hudson River Landing was due to a combination of piloting skill and an autopilot system that was engaged right till impact and kept the plane in a controlled descent within a safe flight envelope. Boeing gives far more control to the pilots and the autopilot plays a smaller role, which may make the same scenario much less likely with a Boeing. Water landings are not a big part of pilot training as there just isn't enough data to simulate the scenario sufficiently, to the best of my knowledge

@AsheeshR Whether it is a Boeing or an Airbus, both could have the autopilot engaged in much the same manner for the flight that you refer to.  In fact, even a Cessna with no autopilot, or an Airbus/Boeing with the autopilot disengaged (or even failed) can be flown by the pilot in a similar manner. It is the pilot's responsibility to keep the aircraft within a safe flight envelope, regardless of what the automation does!

@Tasos Airliners have to be certified to float. See Why would an airplane be approved for ditching?

@AsheeshR: it doesn't matter about the chances so much, rather the possibility of doing so -- it isn't impossible, nor are the chances extremely remote in calm conditions (storms are another story).

@Lnafziger I didn't say it isn't the pilot's job; just that the workload is supposed to be decreased by automation, which in turn allows more focus to be put on the problem at  hand.

Jack lemon Film "Airport '77" :)

@AsheeshR Well, the autopilot in a Boeing can be used to reduce the workload as well.  :)

@AsheeshR Your comment prompted a question: How, exactly, did US1549 land on the Hudson?


text:
What does "design-induced pilot error" means?
In the Slashdot article Is the Tesla Model S Pedal Placement A Safety Hazard? it says:

what aviation analysts call a 'design-induced pilot error'

I tried to search for design-induced pilot error on Google, but found things too complex to understand! What does this mean?

In the link in that slashdot article, it's explained pretty clearly. It's near the top of the article, in short paragraphs tailored for even the most ADD of us. "I wrote that the close pedal spacing of the Model S had contributed to my mistake--a phenomenon known in the industrial world as “design-induced operator error.”"

The phrase is basically saying that bad design causes people to make mistakes.
Design-induced - the interaction design or user experience is problematic.
Pilot error - the pilot made a mistake.
An example of this would be the placement of a flap handle next to a gear lever, making it possible to raise the gear rather than the flaps after landing.
Engine controls in modern designs now feature different shapes for each control knob for similar reasons. There have been many accidents where pilots have grabbed a mixture knob — and shut an engine off completely — when they meant to grab the throttle and reduce power. Different textures and shapes make that harder to do:

An (in)famous example would be John Denver's crash in an experimental aircraft, costing him his life.
Due to the placement of the fueltank selector, which was different from usual, he inadvertently selected an empty tank, causing him to eventually crash as his engine failed from fuel starvation at low altitude.
http://www.avweb.com/news/safety/183015-1.html?redirected=1


text:
What are the pros & cons of Autobrake?
What are the advantages/disadvantages of an autobrake system? In particular I am interested in the Fokker 100 system.
Have any studies been done for the F100 autobrakes and the affects that this system has on the landing gears?

Autobrake is a smart system which basically implies that the pressure is applied to the brakes when a set of circumstances are reached, such as when the plane detects that it is on the ground and the thrust is in idle.
There are in principle only advantages with an autobrake system, since it reduces pilot workload during the moments after landings and reduces necessary runway to stop. While autobrake has what I know not been the reason for any accidents, the faulty computer logic of the computers in the autobrake and spoiler system contributed to a Lufthansa accident in 1993.

As I gather, the Fokker 100 autobrake will be activated when the thrust levers are commanded to idle reverse and the system is on. It has 5 settings: RTO (Rejected Takeoff), OFF and LO/MID/HI, the latter 3 representing the amount of automatic brake pressure.
Autobrake is closely related to the spoilers, which are simply a button on the Fokker 70/100. The direct effect of spoilers on the landing gear is that they are pushed harder down onto the runway (since the lift from the wings is disrupted), making the braking more effective early on during landing.
Source (not very good but the best i could find)

I don't know for certain about the Fokker, but most autobrake systems are designed to produce a specific rate of retardation, using the equivilent of ABS and antiskid, which greatly increases passenger comfort. The effect of opening and closing spoliers, flaps and reverse thrust are all compenstaed for automatically so the pilot does not need to worry about adjusting braking force to maintain smoothness at a time of maximum stress.
The disadvantages are that it is a system and can fail which is why every landing check list includes "Verify Autobrake Operation".
Less obvious advantages include reduced wear on braking systems, reduced tyre wear, automatic compensation for single wheel lockups etc.


text:
How does autobrake work?

An autobrake is a type of automatic wheel-based hydraulic brake system for advanced airplanes. The autobrake is normally enabled during takeoff and landing procedures, when the aircraft's longitudinal deceleration system can be handled by the automated systems of the aircraft itself in order to keep the pilot free to perform other tasks - Wikipedia

How does the aircraft "know" when is time to activate the autobrake
systems on a rejected takeoff and landing?
Does it apply full brake to all the aircraft's wheels?
Is it really used by commercial jets?

Not all commercial jets have autobrakes, and the ones that do usually have a company policy dictating when it will be used.
The criteria for activating the brakes are different depending on the manufacturer and model of aircraft, but are typically some combination of:

System must be armed
A certain takeoff power setting must be set by the throttles
A certain airspeed must be obtained
Thrust levers must be pulled back to idle
Aircraft must still be on the ground

Usually for a rejected takeoff it does use max braking, however the autobrake usually has different settings for landing along the lines of "light/medium/max" braking.  Each setting will use a different amount of runway for landing, much like lightly pressing on the brake pedal in your car versus jamming it to the floor.

Modern Boeings (I know 737, 747 and 777) have an "RTO" auto brake setting.  E.g. for 777, with all of the criteria Lnafziger mentions, max braking is applied if the throttles are retarded above 85kts.  In other words, standing on the pedals will not stop you more quickly.


text:
What type of microcontrollers are used in large scale UAVs?
What type of microcontrollers (in terms of processing power, clock speed) are used in large scale UAVs such as the Northrop Grumman RQ-4 Global Hawk, the General Atomics MQ-1 Predator etc. ?
Also, are smaller, low powered microcontrollers used for controlling subsystems such as the INS and control surface movements. If so, then in what range does their processing power and clock frequency lie?

I think this information is likely to be classified, at least for the specific models referenced.

Yes, thats likely to be the case, however i am looking for a range of parameters for microcontrollers used in large scale UAVs.

Airbus used standard Intel 80186 and Motorola 68010 CPUs with 2.5MiB of memory in the FBW system for A320. Exactly the same chips that were used for computers at the time (around 1985) so they were not expensive and were already tested. Over time they upgraded to newer version of those CPUs. Each computer is composed from two boards with different CPUs, one produces the control output and the other verifies it and shuts the unit down if they disagree. The boards run different standard embedded operating systems and the software was written by two independent teams to minimize risk of the same failure mode in both boards.
Each board only does a little bit of work and the important units have backups. There are 4 units processing the sidestick input, 3 controlling elevator and ailerons, 3 controlling spoilers and elevator trim, IIRC 2 for yaw damper (FAC), 2 for each engine digital control, 1 for each display etc.
The requirements didn't really increase much since then. It is still desired that the tasks are split across many independent boards to minimize effects of one of them failing. So a CPU with few MHz clock rate and few MB of memory would still be able to do the job. But such slow chips are not manufactured anymore, so they are probably using whatever was most common chips few years ago.

I'm not sure if I'd say that either the 80186 or the 68010 were particularly common in computers. Wikipedia: "Few personal computers used the 80186, with some notable exceptions" and "The 68010 was never as popular as the 68000".

@MichaelKjörling: I suppose they picked it at the time because then performance did matter so they needed to take the faster chips that were not used as much. Since performance grew fast since then, modern designs can choose better tested chips over faster ones.

@MichaelKjörling: Still the point is that it was not special chips but general purpose ones that were already on the market.

Absolutely Jan, I'm not disputing the point you made (apologies if my comment came across as if it did), and the chip families were certainly common in computers at the time even though those particular models might not have been very widely used.

As Jan Hudec mentioned, advances in computing mean that off-the-shelf commercial processors offer plenty of computing power for use in UAVs or other aircraft.
Looking at a couple of examples:
The Rockwell Collins IPC-8303 computer uses an Intel Pentium-M 738 at 1.4 GHz, 2 MB L2 cache, 10 watts. There is also a PowerPC option.
The Rockwell Collins FMC-4000 mission computer is able to accommodate a variety of processors:

Quad core PPC 1.5 GHz
Dual core PPC 1.3 GHz
Single core PPC 7448 1.3 GHz
Single core PPC 8315E 600 MHz

They also mention that other components such as Intel Atoms or i7 Dual/Quad core processors can be added.
The amount of information processed by these computers has increased along with their power. The FMC-4000 can use a 10-gigabit uplink. Modern computers are designed to process all kinds of sensor data. For aircraft like the MQ-1 or especially the RQ-4, there are many sensors, including video data, feeding into these computers. They are capable of much more than the first flight computers.
Also mentioned by Jan Hudec, the key in aerospace systems is redundancy. Each subsystem is generally controlled by multiple computers. This ensures both accuracy and reliability, and prevents the whole system from going down due to one computer failing.


text:
What is the relationship between mountain breeze and air pressure?
I am studying for my PPL and am having some problems understanding the mountain breeze phenomenon, especially when it comes to my understanding of pressure.
Basically, I've read that during the day mountainsides get warmer, resulting in the air flowing upwards. While at night this mechanism reverses : mountainsides get colder, and the air therefore flows downwards.
I could be ok with this, if I hadn't been told earlier on by my physics teacher, that in general high pressures tend to flow towards lower pressures. I.e warm temperatures flow in the direction of cold temperatures. This would imply that the breeze has to travel the other way around.
I can't really wrap my head around this. How can I reconcile both concepts ?

High pressures flow toward low pressures, but how are you equating that with warm temps flow toward cold temps?

There is nothing to reconcile: the higher pressure is where the cool air is. The weather report shows pressure fronts, and the low pressure ones are the ones heated up by the action of the sun.
If the mountainside warms up, the air in contact with it warms up. Warmer air has a lower density and it wants to float upwards, like a hot air balloon on a cold day. Meanwhile, surrounding air not heated up by the mountainside flows into where the heated air was, going from cool to hot. The reverse happens when the mountainside cools down: air gets denser and it wants to sink - when it hits the mountainside it just follows that down.
In a vessel with a constant volume, the higher pressure is at the hotter gas. In the unlimited volume of the atmosphere, the gas can expand as it pleases.

The last sentence pretty much nails it. Thanks.


text:
How are composite materials on aircraft joined?
Answer for the question Why are planes using rivets & not welded construction? describes why rivets are preferred for joining aluminium alloy components. But how are carbon-fibre-reinforced plastic components in new aircraft joined?

duct tape? Or was it superglue?

Ideally, fiber composites are bonded and connected by a scarf joint. The scarf ratio is determined by the ratio of fiber tensile strength and the shear strength of the resin. If your fiber takes 3000 N/mm², the resin transmits 20 N/mm² and the fiber content is 60%, the ratio is 1:90, so a 1 mm thick composite layer would need to be joined over a length of 90 mm. In reality, such a ratio is impractical to achieve, so lap joints are used when accepted by the certification authorities. This is the case for for composite gliders, where you will find both scarf and lap joints.
In the early days of powered composite aircraft, fiber composites were seen with the experience of aluminium in mind, and treated with the same methods. Therefore, the Lear Fan and its contemporaries had to use rivet joints throughout the structure. The idea was that by riveting the airframe could be more easily disassembled for inspection and repairs. Riveting carbon fiber composites is quite problematic: You need to use expensive titanium fasteners because aluminium rivets would quickly corrode when in electrical contact to the electrochemically much nobler carbon fibers. Drilling and countersinking holes cuts the very fibers which you try to connect, so you have to double up on wall thickness what is destroyed by the riveting. But the FAA still insisted on rivets - even stringers on panels were riveted, when bonding would had been the most sensible solution.
Aircraft engineers have an expression for composites that are treated like metal: Black Aluminum. The LearFan was pure Black Aluminum. Many of the engineers in this project ended up with Beech when they produced the Starship, so many of the same techniques were transferred as well. At least, the Starship had a fuselage shell which was laid up on a mandrel and then cut just aft of the cockpit section to get the mandrel out. The splicing of the two fuselage sections was then done by a tapered lap joint; if you want, a practical way of making a not-quite scarf joint.
Today we have a new generation of engineers who slowly accept that the nature of composite structures requires their own methods of treatment. But you will still find riveted joints even in modern composites structures. Old habits are hard to break.
A good reason for riveting is to avoid peeling at the edges of a bonded joint. Engineers with no experience rivet their composites, once they gain some experience they switch to bonding and with lots of experience they add rivets again.

The "Black Aluminum" design/construction using rivets is particularly ironic when you consider the Grumman AA-1 series aircraft, which used a bonded aluminum construction.

This is quite fascinating, especially considering the state of carbon fiber construction in auto racing. Formula 1 car tubs (frame), skin (bodywork), suspension and even gearbox casings are made entirely of carbon fiber, and I doubt you'll find a rivet anywhere. While there are considerable differences in loads between a car and plane, the cars will undergo 2G acceleration as well as 5G braking and cornering forces, and the crash test requirements are even higher.

@FreeMan … but they can design without the need to please the FAA. Big difference!

Quite true, Peter. I'm just surprised that the FAA requires riveting despite the fact that F1 cars can take impacts like this and the drivers just walk away.

@FreeMan: At that time, there was little experience for a safe judgement, and bureaucrats have to play it safe. Most studies by US companies had indeed used composite panels just like sheet metal. In Germany, gliders had been built the "right" way 20 years before, but Americans like to stick to their own results. As I say, it takes a new generation of engineers to get it right.

As one who was specifying jo-bolts as high tech fasteners back in the late 1950s, this answer makes me feel really, really old.

One addition to what Peter Kämpf said:often you install "Chicken Rivets" at the end/run-out of a part, just to be sure that no peel-off happens (those areas seem to get out-of-plane loads if not designed properly)  And then finally: the authorities do not like them, as it is difficult to prove with non-destructive testing, that the bond is really good. @FreeMan: there is a difference to a F1 car: you use it for one racing season, but you use the aircraft for many many years and you still need to ensure, that nothing peels off.Fasteners can fail one after the other but a crack can grow suddenly

What about 'Iron Bridge'?
Source: Wikipedia
joints were similar to what a carpenter would use.  So using traditional method for a new material, iron.  They seem to be doing the same with carbon fiber.
http://www.bbc.co.uk/history/british/victorians/iron_bridge_01.shtml
Time lapse videos of 787 show riveting for the main fuselage.

Not so much an answer as a comment, but nonetheless an interesting example of the universal trend to apply old methods to new materials.  Plastic was the same: initially, they'd make a big block and machine it to shape.

In composite structures, rivets are used instead of bonding   not because of superior performance. Properly designed bonded joint is always stronger than the best riveted or bolted joint.
The main reason for using rivets or bolts is that the LONG TIME performance is predictable, while bonded joints may be subject to deterioration due to environmental factors.
It is better to have a riveted joint with 50% of maximum theoretical strength (which retains its load capability for the entire service life),than have a superior bonded joint which may deteriorate.
Also - as a side issue - bonded joints are practical only up to certain thickness, above which it is better to use bolts.

Bonding is normally done with the same resins that form the composite matrix. So will those matrix materials mysteriously not deteriorate while the joint will rot away? No, rivets in bonded joints are used to avoid peeling.


text:
What makes intentional low or missed approaches legal?
A common procedure in flight training is the low approach: simulating a landing, but without actually making contact with the ground before powering up and either going around in the traffic pattern or executing a missed approach procedure, sometimes after flying all the way down to an approach's minimums.
In this situation, a pilot flies very close to the ground - one suggested crosswind training procedure suggests flying along the runway low enough that "[i]t's OK if the wheels inadvertently touch down during the exercise."
Contrast this to other operations, including a simulated engine-out procedure away from an airfield. These are governed by FAR 91.119:

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
(a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.
(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

Training for missed approaches and going around are important for basic skills, and they are performed very frequently. However, the regulations make no exception for training. For a maneuver where a pilot descends below 500 feet AGL without intending to land, is there legal guidance that makes this OK near a runway, or is it an unwritten exception?

This is an interesting one - I was able to think my way out of (a) and (c) pretty easily, but (b) can be tough - the approaches to my home field put you over "congested areas" below the minimum altitude per the regs.

Is there really, truly, such a thing as a go-around that is designed to be done, on purpose and as a part of a pattern? Seems to me, that intentionally done or not, what the pilot is ACTUALLY doing is landing, and then performing the go-around, which is PART OF the landing. Isn't the go-around the transition from landing back to pattern flight?

@CGCampbell you could make a cogent argument for go-arounds being a landing, but the "make a low pass, keep the wheels a foot off the runway" method of improving students performance in the flare is certainly not intending to land. Practice instrument approaches can bust the altitude restrictions above if flown all the way to decision height (as is pretty common) like Articuno mentioned.

Well, I'm going with "It's a written exception, but nobody thought to include it in 14 CFR 91.119 though".
I say this because there are a number of regulations that require a student pilot or applicant for a license to receive and log flight training for go-arounds.
For example:

14 CFR 61.87 - Solo requirements for student pilots
14 CFR 61.98 - Flight proficiency (Recreational Pilots)
14 CFR 61.107 - Flight proficiency (Private Pilots)
And others

The complete text of the private pilot SEL requirement (and they are all similar) is:

§61.107   Flight proficiency.
(a) General. A person who applies for a
  private pilot certificate must receive and log ground and flight
  training from an authorized instructor on the areas of operation of
  this section that apply to the aircraft category and class rating
  sought.
(b) Areas of operation.
(1) For an airplane category rating with a single-engine class rating:
(i) Preflight preparation;
(ii) Preflight procedures;
(iii) Airport and seaplane base operations;
(iv) Takeoffs, landings, and go-arounds;
(v) Performance maneuvers;
(vi) Ground reference maneuvers;
(vii) Navigation;
(viii) Slow flight and stalls;
(ix) Basic instrument maneuvers;
(x) Emergency operations;
(xi) Night operations, except as provided in §61.110 of this part; and
(xii) Postflight procedures.

There aren't any rules that explicitly allow it, but you are practicing landing, so you can do what's necessary for landing.
Also, a common misconception with the minimum altitudes rule is that 500 feet AGL is the lowest you can go over uncongested areas.  That is not so, you can be 1 foot off the ground as long as you can still safely land if your engine dies and are still 500 feet away from structures, etc.  Most airports are in uncongested areas and don't have anything within 500 feet of the runway.

@Articuno The reference is cited in the question. (91.119(c): over open water or "sparsely populated" areas" you can fly as low as you want as long as 91.119(a) is satisfied). I don't agree that most airports are in "sparsely populated" areas though -- Many are, but here in the northeast you're usually flying over residential or industrial developments...

@Articuno Anecdotally I would say "you can't fly below 500' AGL" is a common enough misconception - I've heard it surprisingly often (especially living in New York where there's a counterexample right on the sectional). The regulation is usually cited correctly, but the folks citing the regulation probably aren't the ones getting the interpretation wrong.

When you're over areas that are somewhere between "sparsely-populated" and "congested", it's assumed that persons, vessels, vehicles, or structures are common enough that we can simplify it by saying you have to be 500ft above the ground in general--and for some reason, the FAA codified that simplification too.

This has not held to be true.  Just recently a well known video vlogger was suspended by the FAA for doing a low pass over an off-airport field he had permission to land on.  He was cited and in his hearing it was upheld that because he didn’t actually land, he violated the only exception that allows you to operate within 500 feet of a person or structure.  Technically, if you intend to land and go-around, you are in violation.  Actually performing the landing operation is a mandatory element.  That ruling has real implications for all of us and none of them are good.

There must be more to that story.

@Khantahr, the only thing more to the story is, unfortunately, that FAA argumentation is rather retarded.

Got a source for that? I've been involved with the FAA before, and that story is lacking.


text:
Do steam-gauge VSIs compensate for altitude?
A Vertical Speed Indicator indicates rate of altitude change. Traditional VSIs use a calibrated leak to measure the rate of pressure change, and therefore the rate of altitude change.
However, pressure does not change uniformly per altitude: in a standard atmosphere, air pressure at 0 MSL is 29.921 inHg, and at 1000 MSL is 28.856 inHg: a 1.065 inHg difference. But 10,000 MSL is 20.577 inHg and 11,000 is 19.791 inHg: a .789 inHg difference. A calculation suggests that a VSI calibrated for sea level and climbing at 1,000 ft/min would indicate 739 ft/min at 10,000 feet.
The airspeed indicator has a knob to calculate true airspeed based on altitude and temperature, but the VSI has no pilot-accessible controls. Glass panel instruments would presumably handle this automatically, but is there any correction for altitude in a steam-gauge VSI?

Interesting question!  While this doesn't answer what you asked, I'll mention that on most, maybe all, large jet aircraft these days, the VSI indication actually comes from the INS, and doesn't use static pressure at all.  The advantages to doing it this way are that the indication is instantaneous and and not subject to any of the usual, or unusual, static system errors.

Research suggests that the current TSO for VSI's is TSO-C8e, which just references SAE (AS)8016A - though the standard costs almost an hour of flight time.

Yes.  It appears to be the case for "steam gauges".  At least for a traditional vertical speed indicator.  It's a great question and not one I had considered before.  At first glance, I suspected you may be right, though I don't ever remember actually learning that.
To prove the theory, one pilot apparently took his airplane with a traditional steam gauge altimeter/VSI up to FL220 and found the following:

=>Your altimeter is perfectly accurate at the airport if you enter your barometric pressure correctly.
=>At the cruise altitude of about 8,500 feet or so, your altimeter is off by about FIVE-HUNDRED FEET.
=>At that altitude, it does not matter much that your altimeter is off, because everyone else’s is off by the same amount, and you are far from the airport, and thus landing.
=>The error always seems to be off in the safe direction: You are always HIGHER than you think. Clearly, when they designed the system in 50’s, they designed the altimeters to follow the most conservative lapse-rate we could encounter, so in real-world flying, we are almost-always much HIGHER than we thought, which must be the safest error we can make.
=>The vertical speed indicator perfectly tracks the PRESSURE-based altimeter, not the true altitude, so the vertical speed indicator can be perfectly used to see how much the altimeter will change over time, the ACTUAL climb or descent rate of the plane is actually considerably DIFFERENT… at high altitudes, by 1,290 parts in 24,000, or just OVER FIVE PERCENT.

Hello, and welcome to the Aviation Stack Exchange! Note that the post mentions the aircraft having a G1000, so while this confirms my theory about glass panels, it unfortunately doesn't help with the core of the question about steam-gauge VSI's.

I added references to steam gauges, those were what the answer was for.  The pilot who tested it, used a tradition, steam gauge VSI and altimeter.  The glass cockpit gauges work differently. I moved that reference to clarify it.

One small addition to Ralph's comment - that's not entirely true for all large airplanes.  Some may use INS.  My airplane uses the air data system but the net effect is the same because the VSI displays a calculated value that the system has adjusted for things like temperature, altitude, sideslip (which has a bigger effect on a small airplane), etc.

Can you please quote or point out where he mentions a traditional VSI? The aircraft in question is a Corvalis TT, which does not usually have a steam-gauge VSI. It'd have a backup altimeter, but that's no help here.

authors: السلطان احمد


text:
Is it technically possible to have nuclear-powered hot-air balloons?
Could a balloon use non-fissile isotope, like Pu-238, to heat air in the envelope to stay afloat for years?
let's put political and health related problems aside, and consider if it's technically possible at all. Say, as an unmanned, high-altitude scientific/weather station.
I know that:

Pu-238 has power output of 0.54 watts per gram
Its half-life is 87.7 years (power output halves after that time).
great most of the energy can be radiated out as heat, and transferred to surrounding air.

I don't know what buoyancy can the hot air balloons provide, and what kind of energy input they require to stay afloat. So - would it fly?

Well, what is the weight for a nuclear reactor for this reaction?

@kevin: 0.54 watts per gram, halved after 87.7 years ; as large as you like, within reason, Likely double the mass due to radiators and thermocouples, also substract 5% as electricity for the probe.

If this is not possible, there is still helium.

well, I could attach it to a nuclear warhead and send it up in the sky for a few brief moments...

Fortunately nuclear-powered bombers and cruise missiles projects were all canceled but unfortunately they are all technically possible.

This question is incomplete due to being unbounded.  What is the development budget for the R&D effort?

The problem with a Pu-238 RTG is that is heavy and low-power. That is to say, the energy is released too slowly.
This is not a fundamental problem. Phosphorus-32 is (as the name indicates) almost 8 times lighter, and it has a half-life of just 14 days. This makes it about 15.000 times more powerful per gram as Pu-238 - 8kW/gram !
Typical burners are 3MW, but run at 20% duty cycle for an average power budget of 600kW. This means you only need 75 grams. You can't realistically have 3MW peak power, as this is not a controllable heat source. And using 375 grams for 3MW sustained would mean that you need to get rid of 2400 kW of power on average.
Practically speaking, this means that you need a heat buffer. This isn't a big issue, as this heat buffer can surround the P-32 and act as shielding - the absorbed radiation would directly be converted to heat. You'd want a salt melting near 373K, as that's the temperature you're aiming for. Such salts do exist, so that's not a big problem.
Technically, this looks feasible. But the practical problem is that your 3MW heat source is a major hassle. It has to be made in a nuclear reactor, and comes out hot - literally. Handling it is a major pain. You need to permanently cool it. That's just not going to be cheap.

Using a short-lived isotope, even if we ignore the whole million of technical problems, sort of defeats the whole point of being nuclear - at that point you're getting better endurance out of a low-density fossil fuel like methane.

Most likely no.
RTG does not have enough power. The burner of the hot air balloon requires 2 to 4 MW of power (here) so you need at least 4 tonnes of Pu to produce that (2000,0000 / 500 = 4000 Kg), assuming 500 W per kg (0.5 W/mg). From the source, a moderate size balloon can lift few hundred kilograms at most.
The true nuclear reactors provide much more power, but they are heavy. Hyperion, for instance, provides 25 MW and weighs 50 tons, so performance per kg is even lower. It could power a cluster of say five balloons, but they would not be able to lift 10 tonnes each.
From the other side, nuclear reactors are probably not optimised for the minimal weight, assuming that just a heat output is required. They are built to match different requirements, so some specially built device may be capable of lifting the balloon.
Lockheed Martin is developing a very promising device.

I wonder if these 2 to 4 MW are the sustained value over the flight, or during the relatively short bursts when the burner operates. Because if you observe a flying hot air balloon, the burners are off most of the time.

"A typical flight lasting 45 minutes to 1 hour, and consume about 20 to 30 gallons of propane" src. LPG energy density 84,250 BTU/gal. src. 30 gal/hour is ~740KW, but that's including initial filling, not just sustained flight.

The amount of Pu required (750,000 / 500 = 1500 kg) would still be above that the balloon could easily lift, and the extra power may actually be required for maneuver.

Without any parameters on what containment is needed, there is nothing you can say about if an actual nuclear reaction could power a balloon. A prompt critical reaction can easily produce vast amounts of power (and irradiate everything in it vicinty) that could easily lift (and incinerate) a baloon. However a feasibly balloon that also has a payload of cargo or living beings is likely not an option due to shielding taking up too much mass.

Reactor also contains parts like cooling system, moderator, even if we do not put any shielding on it.

Probably not from decay heat as others have said, but ignoring the minor matter of the radiation and toxic byproducts it is clearly doable with a fission pile burning sufficiently enriched fuel.
The Soviet nuclear program has had at least one criticality accident with a PU core that ended up in a sort of equilibrium between its thermal expansion and reactivity, so say 10kg of fissile material and a load of heat spreaders to get the heat out into the air, bet you could do it with 50kg or so of machine (But I would not want to be the guy to have to go in and shut it down).
There was a proposal for a Venus probe using a nuclear ram jet that may be applicable, thing is once running there was no good way of stopping it because the decay heat would melt the core.

Do you have sources about the Soviet program & Venus probe ? I'm interested

I agree, and I think that the weight could be quite a bit less than 50kg. Critical mass is as low as 10kg for some fuels. And graphite foam is extremely lightweight yet has extremely high thermal conductivity, so an effective heat spreader might only add a couple of kilos. Besides the fuel and the heat spreader I don't see that much other equipment is necessary, beyond a means to control the reaction rate, probably a simple neutron reflector.
If unmanned, then no shielding necessary. If manned, one would simply need to have very long tethers between the balloon and the gondola.

It is unlikely that a balloon could use Pu-238 to heat enough air in the envelope to get airborne since Pu-238 is not powerful enough for that.  What would come a little bit closer is some much more powerful radioisotope such as Cobalt-60 for example and that one will produce more than 13 KW/kg through its first years of decay.

Welcome to Av.SE. While this is interesting discussion, I don't see an answer to the stated question here. This being a Q&A site, we require "answer" posts to do that. Can you expand on these thoughts to give a conclusion, that a nuclear hot air ballon is or isn't hypothetically possible?


text:
What airline academies are available to US citizens?
It seems that EU/Asian/Middle Eastern citizens have the opportunity to apply for several self-funded programs which (upon acceptance and completion) guarantee a job as a first officer on small twin engine aircraft flown by the sponsoring airline. Is there any such program available to US citizens? And if so, what makes an applicant competitive?

There are flight schools that do offer guaranteed jobs afterward. The flight schools will work with minor airlines and if you get 300-500 hours flight time at the school you can interview with airlines and they might offer you a job and a $11,000 tuition. This is what I plan on doing. Atp offers this https://atpflightschool.com/airline-career-pilot-program/

Are you asking if a) a US citizen can apply to those foreign programs, or b) there are similar programs in the US itself?

Many of the Asian ones are only open to their own nationals, to give them the opportunity to become a pilot as well. Pilots are in demand, and particularly captains are hard to find. For the funding, many F/Os are now self funded, low cost airlines do usually not fund initial pilot education.
An outfit like Stella Aviation in The Netherlands did offer bank loans to fund the license, guaranteed until the student found a job.
Unfortunately, we don't see many USA citizens working as expats: they are often very expensive due to having to pay double taxes when working abroad, USA has historically had few tax agreements with other countries.

USA has no tax agreement with any other country https://www.irs.gov/businesses/international-businesses/united-states-income-tax-treaties-a-to-z

@MJeffryes ah right a sweeping statement. I've amended the answer.

Actually the US has many double tax agreements with other countries. The issue is that they expect their citizens to keep paying US taxes even if they are living and working entirely abroad.


text:
Constant TAS versus constant GS: What is the influence on turning circle?
Scenario
Lets imagine a 50kts wind from east.
Now lets imagine an aircraft flying at 200kts (True Air Speed) east that make a 1.15G turn -90º to north. Maintaining in all moments the given constant speed.
Now, lets imagine the same flight but with 200kts constant ground speed.

In the first case, the speed is 200kts TAS= 150kts GS, and after the turn TAS=GS=200kts
In the second case, the speed is 200kts GS = 250kts TAS, and after the turn, TAS=GS=200kts
Any mistake until now?
The question:
The question is how that influence the turning circle? In which of the two cases the turning circle is flatten/stretched and in which is circular if any? What is the approximate shape of them?
Further explanation
Considering my very weak understanding, the turning circle G depend on absolute speed (~ Ground speed), and thus, turning with a constant ground speed imply a circular turning. Which is independent of the wind. Of course, the pilot would have to accelerate/decelerate to maintain this speed.
With TAS, the real speed is variable, so in our case, I expect to see a turning circle which is horizontally flatten.
But, using a planning system, the result I observe is the reverse: the circle is constant (independent of wind, circular) on TAS and variable (dependent on wind, shape is not drawn) in GS.
Edited: TAS=GS=200kts: I just realized that it is not really true, cause the aircraft need to head slightly east to compensate the wind, so probably the TAS will be ~206 and GS 200. Even if that do not make a big difference for the question.

Hello Adrian, welcome to Aviation.SE!

At the end of your turn, is your heading or your track angle North?

I would say track, but I guess any would fit as an example. :-)

You are missing what bank angle you are turning at.  Rate of turn is predicated on true airspeed while radius of turn is predicated on groundspeed.  If the bank angle is constant for the constant GS exercise, the TAS would make it non-circular.  If you vary the bank angle with TAS, the radius will be a perfect circle.

@wbeard52 I though G and Bank-Angle was nearly equivalent. In any case, yes, I am supposing a model in which the turning bank-angle is constant.

To better understand the physics of a turn, maybe it helps to look at the centripetal force in a different way. This force is actually pulling the aircraft sideways into the new direction of movement. When banking into the turn on an easterly course, the centripetal force will accelerate the aircraft to the north and, towards the end of the turn, will decelerate its easterly speed, such that it will have a northerly speed when the turn is complete. The centripetal force is the means by which ground speed gets converted from a purely easterly speed to a northerly speed.
If you fly with 200 kts in a 50 kts headwind and want to fly a northerly track after finishing the turn, you simply stop turning after having decelerated the aircraft by only 150 kts. You don't fly a quarter circle of 90°, but only one of 75.5°; the angle where the cosine has shrunk to 0.25. After that, your easterly speed component is reduced by 150 kts and your northerly speed component has increased to 193.6 kts. When viewed by another plane flying in the same headwind, you have flown a segment of a circle measuring 75.5°. When seen by an observer on the ground, your ground track is a compressed circle segment.
Starting with 250 kts will make you perform the turn at a higher speed, but with the same technique.

Any mistake until now?

Yes! Your assumption that your ground speed would be 200 kts is wrong. At all times, you will maintain a TAS of 200 kts, and the ground speed after the turn in the first case is only 193.6 kts.
In the second case, you start with a TAS of 250 kts and maintain that over the full turn. Your ground speed after having achieved a northern track is now 242 kts.

The question is how that influence the turning circle?
  In which of the two cases the turning circle is flatten/stretched and
  in which is circular if any? What is the approximate shape of them?

That depends on the observer. Your ground track is compressed in easterly direction because you started at an easterly speed component of 150 kts but used the aerodynamic forces of 200 kts for turning. You stopped turning after having yawed the airplane by only 75.5°, so you now fly a correction angle of 14.5° to achieve a purely northern track. The observer will see you accelerate from 150 kts ground speed to 193.6 kts ground speed (and from 200 kts to 242 kts in the second case).
The shape of the circle will only look round for an observer flying in the same headwind.
In a tailwind, you would keep turning until you have completed a circle segment of 104.5°, so you can let the centripetal force act longer in easterly direction for a ground speed change of 250 kts in easterly direction. Since it will reduce the aircraft's northerly speed component over the last 14.5°, the centripetal force will slow the northerly speed component to 193.6 kts over the last 14.5° of the turn after it had reached 200 kts after turning 90°. Now the ground track is stretched in easterly direction.
Below I added a graph with three ground tracks and airplane symbols overlaid to show the correction angle at the specific point of the turn. All three cases perform a 90° turn and fly initially parallel to the wind direction. I used 50m/s TAS and ±20m/s wind speed; the axes are in meters. The blue line is the case without wind.

Ground track when turning in wind (own work). A turn from a headwind course takes much less time and azimuth change than one from a tailwind course. Only the ground track without wind is a circle, all other ground tracks are ellipses. In the headwind case the axis parallel to the wind direction is the shorter axis and in the tailwind case it is the longer of the two axes of the ellipse.
If you insist on keeping the ground speed constant, you will need to speed up when turning into the wind rsp. to slow down when turning out of the wind. Your second case with 250 KTAS while heading east and 206 kts when flying a northern track is very unusual. This answer gives you the basic equations. The time to fly a 75.5° turn with 30° bank angle (= 1.15 g) is $$t_{75.5°} = \frac{v\cdot\pi\cdot75.5°}{g\cdot\sqrt{n_z^2-1}\cdot180°}$$
which yields 30.4 s for 250 kts (= 118.6 m/s) and 25.1 s for 206 kts, so you will spend 27.75 s turning when the deceleration is linear. The deceleration along the flight path is 0.455 m/s², so you will need to throttle down during the turn and throttle up when the deceleration phase is over. Good luck keeping the ball centered while turning and changing the p-factor at the same time!

"In the second case, you start with a TAS of 250 kts and maintain that over the full turn. Your ground speed after having achieved a northern track is now 242 kts"
That is the case 1 with different speed. Case 2 is: you fly constant 200kts GS, meaning a TAS gradient (non-linear) between 250kts to 206kts

@AdrianMaire: If you want to fly constant GS in wind, you will need to change airspeed while turning. Where do you take the power to do so? Or the drag to slow down quickly enough? Do you accept to dive or to climb to speed up/decelerate? This is highly unusual; what I describe is what you get taught in flight school and what most pilots do.

well, it is a model, so I do not care really about how easy is to fly it. It is more for understanding theoretical behavior for a software. If the Pilot do not want constant GS, he just has to set TAS, or plan GS and fly an approximation. You could also guess a special futurist aircraft that is able to electronically maintain GS by adjusting engine and aero-brakes.

@AdrianMaire, it is not as much about hard as about only possible up to certain limit. While the wings can generate significant force, and thus acceleration, perpendicular to the relative wind (all aircraft can withstand at least 2.5G, of which 2.29G can be directed sideways in a level flight in suitable bank), you can rarely generate more than about 0.3G forward (thrust-to-weight 1:3) and even less backward (speed brakes are not all that effective)). So in a strong wind, you can only maintain ground speed in a rather loose turn.

If you maintain a constant bank angle (30 degrees for a 1.15 g turn) and maintain constant true airspeed of 200 Knots, your path will be as shown in the chart by the yellow line.
If you maintain a constant ground speed (150 knots) and a constant acceleration 1.15, then your path will be as described by the grey line. It will be as if there is no wind, however it requires thrust variations and bank angle variations.

The radius of the turning circle depends on the True Air Speed, not the Ground Speed. TAS is the true measure of aircraft performance and is used in  every situation when actual performance needs to be measured.
Consider the forces on an aircraft in a coordinated turn with a banking angle of $\phi$

Image from code7700.com
Now, the load factor n on the aircraft is simply the ratio of the lift to the weight.
$n  =  \frac{L}{W} = \frac{1}{cos\phi}$
The centripetal force acting on the aircraft can be given by,
$F = L sin\phi$,
which is equal to,
$F = m . \frac{v^{2}}{R}$,
where $v$ is the TAS and $R$ is the radius of turn.
Solving, we get,
$R = \frac{v^{2}}{g . tan\phi}$,
or in terms of load factor,
$R = \frac{v^{2}}{g . \sqrt{n^{2} - 1}}$
Note that in all these cases, the velocity $v$ is the TAS, not the ground speed. So, for a 1.15g (or n equals any other value) turn, greater the speed, bigger the turn radius, at a constant bank angle.

I'll just list out the various speeds used for qualifying aircraft performance

Indicated Air Speed is the the speed of an aircraft as shown on its pitot static airspeed indicator, calibrated to reflect standard atmosphere adiabatic compressible flow at sea level. Simply put, it is what the airspeed indicator shows.
Calibrated Airspeed is the indicated airspeed corrected for various errors (like instrument and position errors)
Equivalent Air speed is the airspeed at sea level in the ISA at which
the dynamic pressure is the same as the dynamic pressure at the true airspeed (TAS) and altitude at which the aircraft is flying.
True Air Speed is the speed of the aircraft relative to the atmosphere. This is the speed used for measuring the aircraft performance. The TAS, along with the heading, gives the aircraft velocity relative to the atmosphere.
Ground Speed is the vector sum of aircraft velocity and wind velocity (at the flight altitude). This gives the speed of the aircraft relative to the ground.

Image from stackexchange.com
The ground speed is rarely used in measurement of aircraft performance directly. The performance measurements are made with reference to the atmosphere as the frame of reference. This means that the True air speed, which gives the velocity with respect to the atmosphere is used.
-------------------------------------------------------------------------------For an observer on ground, the turn will be a circle if the TAS is equal to the ground speed i.e. if there is no wind.
If there is a head wind, the turn will be squeezed i.e. the turning circle will be egg shaped, with the squished side in the direction of motion. For tail wind, the squished side will be in the opposite direction.
The case where headwind is equal to TAS is the limiting case- basically, the aircraft will appear to the ground observer to turn along a line.
It will be like some one on shore seeing a swimmer turning in a water body where the water currents vary.

Great explanation, thanks you a lot. I still have a question to understand fully: Why in the centripetal force formula (F=m*v^2/r), you interpret v as TAS and not absolute speed? I mean, for lift the important speed is TAS, but for centripetal force, i would expect Real speed. E.G supposing 100kts head wind and 100kts aircraft TAS speed, the aircraft is currently not moving, so how could he need a radius to turn (meaning infinite turning time)? Instead I would expect 0 bank-angle turning over itself.

Sorry if I sound pushy, that is not my intention. I just do not want to lets any understanding hole.

@AdrianMaire I think you've answered the question yourself. Taking ground speed means you've selected the wrong frame of reference. If you consider TAS = headwind, the aircraft is not moving wrt ground, and should not require any thrust. But it does.

@AdrianMaire Centrifugal force is an inertial force, meaning that it is caused by the motion of the frame of reference itself and not by any external force. For example, if one stands on the ground and watch children spinning on a merry-go-round, then in the stationary frame of reference their outward acceleration is caused simply by their inertia. In our frame, which is external to the rotating frame, there is no centrifugal force at work. But in the rotating frame of reference of the children, there is a centrifugal force.

@AdrianMaire For an object in a circular motion, the object must be accelerating towards the center of rotation. The object has a tangential velocity in that frame of reference.

False: "TAS is the true measure of aircraft performance and is used in every situation when actual performance needs to be measured." Nearly all limitation and performance data in the POH/AFM is based on indicated airspeed (source PHAK, 8-2) is in  indicated airspeed.
https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2008.pdf

Ignoring the wind::
Your first case has a constant TAS, so you should expect a constant radius (i.e., circular) path.  (Speed isn't changing, bank angle or 'g' isn't changing, so constant radius)
Your second case requires the plane to reduce its TAS from 250kts to 200kts without changing the bank angle.  That will affect the no-wind path to make a "decreasing radius turn".   (@Aeroalias's answer shows the relationship between radius and velocity). For a given bank angle, a lower air speed will result in a smaller turn radius.  Imagine a 1.15g turn in the SR-71 vs the same 1.15g turn in a Piper Cub.  Since you're slowing down during the turn, your no-wind path will look more like the letter "J" than a quarter-circle.
Not ignoring the wind:
Up until now I've talked about the no-wind situation, because the airplane doesn't really know or care about the ground.  It's just swimming through a large mass of air.  "Wind" is what we call that air mass when is moving relative to the ground.
For the first case, the wind will "squish" the ground track of the latter 1/2 of your turn to make it somewhat "J" shaped.
For the 2nd case, the wind will "squish" the ground track of the latter 1/2 of your J-shaped turn to make it appear to be sharper (less circular).

with a 50 knot westerly, its not going to be constant radius, relative to the ground.  it will be declining radius.  as the plane turns, it will get pushed further downwind. remember your turns around a point, and the change in bank angle to keep a constant distance? http://www.flightsimbooks.com/flightsimhandbook/93-1.jpg

@rbp - Isn't that what I said, in the part starting with "For the first case,..."?

your answer is not very clear. one thing that might help would be to edit the question itself so the cases are clearer, and then answer each case


text:
What is the procedure to obtain an FAA ATP while in the United States for a holder of a CPL from Pakistan?
I hold a CPL from Pakistan and currently fly an A320. I have accumulated over 4000 flight hours. If I visit the United States, what is the procedure to obtain a FAA ATP certificate?

Your question is more or less answered here. You need to be in the US legally (visa, green card), get TSA approval (if necessary) and be able to pay for your training.

@Pondlife I think that he wants to convert his foreign license to a US license.

While this question covers converting an EASA license, the process is the same.

@Lnafziger Good point, that could be it. But I don't think the question you linked to applies either: you can only get a private certificate under 61.75, not an ATP. For an ATP he still has to do the tests, at least according to 61.153.

There are many things that need to be accomplished.

Get a letter of authenticity from the FAA validating your license is valid and from an ICAO contracting country.
Study and pass the ATP multi-engine written test.  You may have to get a graduation certificate from a school offering the CTP course.
Apply for and receive TSA clearance.
https://www.flightschoolcandidates.gov/afsp2/?acct_type=c&section=WN
Take the FAA ATP practical test in an A320 airplane or FFS simulator.  It is best to contact a training center on what is required.

authors: Αλέξανδρος Δαμανάκις


text:
Where can I find standard aviation abbreviations for the "unit of measure"?
I have been in the aviation industry specialising in Logistics all my life.  There used to be a standard, the ATA 200, for how to abbreviate the unit of measures, such a EA for each, KG for kilograms, HU for hundred, and so on.  I understand that the ATA 200 is now dead and has been replaced by ATA Spec 2000 but I can not find these abbreviations in the Spec 2000.
I suppose that these abbreviations are still valid but where can I find them?

Hello Erik, welcome to Aviation.SE!

This is defined in ICAO Annex 5 - Units of Measurement to be Used in Air and Ground Operations